Treatment of copper-oxide rectifiers with nitrogen



Patented June 1,

TREATMENT OF COPPER-OXIDE RECTI- FIERS WITH NITROGEN Earl D. Wilson,Wilkinsburg, Pa, assignor to Westinghouse Electric & ManufacturingCompany, East Pittsburgh, Pa., a corporation of Pennsylvania No Drawing.Application September 26, 1941, Serial No. 412,423

6 Claims. (Cl. 175-366) My invention relates to copper oxide rectifiersand, in particular, relates to manufacturing methods for producingstable and invariable electrical characteristics in such rectifiers.

It has been found that copper oxide rectifiers produced by prior artmethods, such, for example, as those described in the United Statespatent to L. 0. Grondahl No. 1,640,335, assigned-to the Union Switch 8:Signal Company of Swissvale, Pennsylvania, have a certain characteristicwhich is undesirable for many purposes, this characteristic being that.what may be termed reverse leakage current" increases rapidly during thefirst few hundred hours of their use. It is, of course, a characteristicof rectifiers generally that they conduct current quite readily in onedirection and oppose a much higher resistance to current flow in thereverse direction; this resistance to reverse current flow is in no caseM- tually infinite. There is always a slight so-called reverse leakagecurrent" and it is to this that the foregoing sentence refers. Sincethis "reverse leakage current represents an energy loss and producestemperature rise in the rectifier, it is desirable that it should at alltimes be as low as possible; the above-mentioned tendency for it toincrease in the course of use is, accordingly, an undesirable thing.

I have discovered thatthis tendency of "reverse leakage current toincrease during use of the rectifier can be prevented by subjecting therectifier discs during their course of manufacture to aheat treatment inan atmosphere of nitrogen. The full detailsof this process will now beexplained. I

Copper elements are .first cleaned by dipping in nitric acid, rinsingwith water and drying in air in the manner described in the above-men-vtioned Grondahl patent. Thereafter they are placed in a furnacecontaining atmospheric air and heated to a temperature of 1025 C. for aperiod of about fourteen minutes. Thereupon the air is quickly displacedfrom the furnace and an atmosphere of substantially pure nitrogensubstituted for it. The elements remain in the nitrogen atmosphere atsubstantially 1025 C. for an additional period. While I have found thateven a very brief treatment improved the rectifier discs and that theimprovement increases with the length of time, at least up to thirtyminutes that the treatment is continued, a treatment of three minutes iseffective enough for most practical purposes and is, of course, moreeconomical as a manufacturing method than longer treatments.

After treatment in the nitrogen atmosphere as above described, theelements are immediately.

removed to a second furnace containing atmospheric air and maintainedtherein at 450 C. for a period of fifteen minutes.

process of preparing the rectifier elements may follow that described inthe above-mentioned Grondahl patent.

I have found that this nitrogen treatment does not appreciably affectthe resistance of the rectifier elements to current flow in their highlyconductive direction, while the resistance to flow of the "reverseleakage currents is increased by a large factor. This treatment is alsoeffective in improving rectifiers which, previous to their oxidation,have been given the high vacuum treat-' similar purposes is within thepurview of my invention,

I claim as my invention:

1. The method of manufacturing rectifier ele-.

ments which comprises oxidizing copper at a temperaturesomewhat belowits melting point for a substantial period, immersing the. oxidizedelement in an atmosphere of nitrogen at'a temperature somewhat below itsmelting point, and thereafter cooling the element.

2. The method of'manufacturing rectifier elements which comprisesoxidizing copper at a temperature somewhat below its melting point for asubstantial period, immersing the oxidized element in an atmosphere ofnitrogen at a temperature somewhat below its melting point, thereaftermaintaining the element at a substantially lower temperature for aperiod of the order of minutes in duration, and thereafter chilling theelement to substantially. room temperature.

' 3. The method of manufacturing rectifier elements which comprisesoxidizing copper at a temperature somewhat below its melting point forasubstantial period, immersing the oxidized element in an atmosphere ofnitrogen at a temperature somewhat below its melting point.thereelement.

4- The method of manufacturing rectifier elev I Thereafter they areimmediately quenched in water. The further taining the element at atemperature or the order of 450 C. for a period of the order of fifteenminutes, and thereafter quenching the element.

5. The method of manufacturing rectifier e1emeats which comprisesoxidizing copper at a temperature of the order or 1025" C. for asubstan-, tial period in an atmosphere of air, immersing the element in.an atmosphere of nitrogen at a temperature or the same order for aperiod of the order of three to thirty minutes, thereafter immersing theelement in an air atmosphere at atemperature of the order of 450 C. fora period of the order of fifteen 'minutes -and thereafter quenching theelement.

6. The method of manufacturing rectifier elemerits which comprisesoxidizing copper at a temperature of the order of 1025 C. for a periodof V the order of fourteen minutes, immersing the elemerit in anatmosphere of nitrogen at a. temperature of the same order for a periodof the order of three to thirty minutes, thereafter immensing theelement in an air atmosphere at a temperature of the order of 450 C. fora period v f the order of fifteen minutes, and'thereaiter uenching theelement.

EARL D. WILSON.

